Stabilization of alkylene glycols



TRON 6F YLENE GLYCOLS Arthur R. Sexton and FrancieN. lilquist, Mid

land, M011" z t Company. M Dela Rio Drawing. Application as ore to Themowfihemical d, Mich, a corporation of S! No. 669,322

i (or. eta-u) r 1 This invention relates to stabilizing lower alkyL eneglycols against thermal decomposition.

In certain types of aircraft and automotive engines, the liquid coolant,instead of running at the conventional temperature of 100 C. or less,commonly circulates at 150 C. in a closed system, and may occasionallyreach 200 C. or higher, perhaps for an extended period. The problem ofselecting a coolant which will operate satisfactorily at thesetemperatures and yet will not freeze even at extreme winter temperaturesis a difllcult one. Ethylene glycol, undiluted or together with a lesserproportion of water, is most frequently chosen as the coolant, but ithas the undesirable property of decomposing slowly at the highertemperatures mentioned to form organic acids, carbon, and

gummy tars. These acids, when formed, tend to corrode the metallic partsof the circulating systern, and the carbon and tar ultimately foul theheat-transfer surfaces and throttle circulation. In consequence. withethylene glycol coolants. periodic over-hauling of the circulatingsystem is necessary, sometimes at short intervals.

In an effort to provide a more satisfactory liquid coolant for operationat high temperatures, it

has now been found that the lower alkylene glycols, such as ethyleneglycol, may be stabilized against thermal decomposition of the typementioned by incorporating therein a small proportion of a benzopyridlneor a monomethylbenzopyridine, e. g. quinoiine, isoquinoline, quinaldine,

and isomers of the latter. These compounds almost completely restrainthermal decomposition of the glycols, both in the undiluted state and inmixtures thereof with the same or a lesser Weight oi. water,temperatures up to 200 C.,\and very markedly retard decomposition evenwhen the glycols are maintained liquid under pressure at temperatures ashigh as 300 C.

Glycol compositions stabilized in accordance with the invention not onlyare useful as coolants for internal combustion engines but aresatisfactory as liquid-heat transfer agents in general at temperatureswithin the range mentioned. rized by extremel low freezing es. as wellas thermal stability. ns may also be used as fluid pressureand poweltransmittlng media.

a ioa'er allzyiene glycois to which the invention is applicable containfrom two through five carbon atoms per molecule. 0f these. ethyleneglycol, and to a lesser extent industrial mixtures of propylene glycoisand of butylene glycols, are of present commercial interest. Suchglycols may be employed according to the invention in the undilutedstate or mixed with a equal or lesser weight of water. With; largerproportions of water. the boiling points of the solutions are somewhatlow for a high temperature fluid, and thermal decomposition is rarely aserious problem.

Both quinoline and isoquinoline, and, insofar as known, any of theirmoncmethyl substitution products, or which quinaldine is the mostcommon. may be employed as stabilizers according to the invention.either as the purecompounds or as crude mixtures containing one or moresuch compounds. Typical of such mixtures are coal-' tar base fractionsboiling in the range of 230 to 270 0., prepared by the iractionaldistillation of crude coal-tar bases produced during the distillation ofcoal in accordance with usual industrial practice. Some bone-oildistillates contain ing benzopyridines may also be used.

The stabilizers of the invention are only sparingly soluble in theundiluted glycols and their aqueous mixtures, but a sufilcient quantitymay be incorporated simply by stirring the stabilizer into the glycolmixture. Alternatively, a stronger solution may be made up in a mutualsolvent, such as alcohol, and the solution stirred into the glycolcomposition. A small proportion of the benzopyridine or its methylhomolog is all that is required to effect stabilization, 0.2 to 5 percent by weight of glycol present being ordinarily satisv factory, withat least 0.5 per cent being preferred.

The benzopyridinej stabilizers, in addition to preventing carbon and tarformation in heated glycols and glycol-water mixtures, also minimizecorrosion of metals by these liquids because of the fact that theyalmost completely restrain development of acidic substances bydecomposition of the glycols. They also function to a moderate dearea asan inhibitor in the conventional sense of retarding the corrosion ofmetals'by other agents, such as air, which may be dissolved in theglycol solution. However, when extremely corrosive conditions are likelyto be encountered, it is prefarable to rely on the benzopyridines asthermal stabilizers only and to introduce in addition a small proportionoi a conventional corrosion in- Since many such inhibitors arethemhibitor. selves unstable or volatile at temperatures of 200 to 388it is important to select an inhibitor which is not aiTected adverselyby heating. Sodium silicate, usually from 0.5 to 5 per cent by weight ofthe glycol, is a preferred choice While the neat-transfer media of theinvention ordinarily consist of the glycol and the stabilizer,

.added as desired.

details are given in the table. The metaltest atthe 'sta V afterpolishing; at the end of the run. The losses aeugsse with or withoutwater, minor proportions oi other ingredients such as anti-roamingagents. leak.- stopping compounds, and dyes. as well as the conventionalinhibitors already mentioned, may be The following examples will serveto illustrate the invention, but are'not to be construed as limiting itsscope. In the examples, a testing apparatus was employed; consisting ofIan electrically heated closed iron chamber of about 400 00. capacityand a circulating system for withdrawing the liquid being tested from areservoir, iorcing it under a pressure of 100 to 120 pounds per squareinch into one endoi the heated chamber. removing it from the other endoi the cham-' her through a relief valve, cooling it, and returning itto the reservoir. The rate oi. circulation was controlled at about 800cc. per hour.

p I solution and apparatus remained tree of carbon. The rates ofcorrosion of the metal specimens were extremely low in all the runs.

Erma: 2.-U..on.ursn Garcon Ar 300 C.

itself decomposes very rapidly at 800 C. The' stabilizers entirelyprevented formation of carbon and all but traces oi tar. Even underthese extremely severe conditions, the marked eilectlveness or thestabilizers, and the low rates of corrosion of the metal specimens, arequite. apparen r Table E it it? (si n) risen) Appearance Corrosion am,

Carbon Brass EXAMPLE l.- 70 PER CENT GLYOOL AT 110' None .s

do (in page:

Isoquin lllJD--. "l. g l msinuomss) OgTlI BB6 (230-m' MPLE a-mo was CENTGLYO None {13.5 LON 7.0 5.8

Quiooline.-..

Isoquinoline Quinaldlne (Crude) l Discontinued because of excessivedecomposition. I Not measured, but specimens appeared unchanged.

Weighed'polished test specimens of aluminum.

Dark Brown" 7 Olesr Dark Brown.

iron, brass, and copper were placed in the heated 4g chamber throughouteach run. The purposes oi the metal specimens were to have present inthe system the metals normally used in liquid-cooled engines and also toobserve the rates 01' corrosion of the metals.

EXAMPLI l.-Aousous Mnzruss AT 200 C.

i In each of the test runs summarized in the table, the system wasfilled with the given volume or a mixture of '70 parts by weight ofethylene glycol and 30 parts or water, to which (except in the case ofthe'biank) 0.5 part of the-stabilizerl listed was added. The chamberwas. maintained tinned for the. period stated. The pH of the liquid'wasmeasured at the beginning and at the close of the run. The appearanceoi. the solution,

at 200 C. and circulation or the liquid was conr a of ethylene glycoland from about 0.2 to about per cent-by'weight or iscquinoline. 4. Aheat-transfer medium chemically stable and the presence of tar and ofcarbon in the.

chamber at the end or the test were noted. These specimens p esent inthe chamber were weighed of each run. and were reweighed,

' gbcol underwent considerable decomposition at 300 C. to iorm'carbon.Each oi the stabilizers eii'ectiveiy prevented deccmpositiom. and theExcessive Eros-in sibls.) (0

Non

Tram

What is claimedis: 1. A heat-transfer medium consisting essentially of alower alkylene glycol containing from 2 through 5 carbon atoms permolecule and not over an equal proportion by weight or water stabilisedagainst thermal decomposition by a 50 compound selected from the classconsisting oi benzopyridines and .monomethyibenzopyridines in aproportion of from 0.2 to 5 percent by weight at elevated temperaturesconsisting essentially 4 .oi' ethylene glycoiand from about 0.2 to about5 .3 per cent by weight or quinaldine.

' 5. A liquid heat-transier'medium chemically stable at elevatedtemperatures consisting essen- ,tlally of one part by weight of ethyleneglycol. not over one part oi water, and 0.002 to 0.05 part of quinoline.

6. A liquid heat-transfer medium chemically -stable at elevatedtemperatures-consisting essentially of one part by weight of ethyleneglycol, not over one part of water. and 0.002 to 0.05 partvisoquiuoline.

'l. A liquid heat-transfer medium chemically v sees (Excessiveou'bonisstlen rendesod measurement iinpos stable at elevatedtemperatures consisting essentially of one part-by weight of ethyleneglycol, not over one part of water, and 0.02 to 0.05 part of quinaldine.

8. In a process wherein a heat-transfer medium consisting essentially ofa lower alkylene glycol containing from 2 through 5 carbon atoms permolecule and not over an equal proportion bywelght 01' water is heatedas a liquid for a prolonged period at an elevated temperature,

the method of minimizing thermal decomposition of the liquid whichcomprises maintaining dissolved therein a compound selected from theclass consisting of benzopyridines and monomethylbenzopyridines in aproportion of from 0.2 to 5 percent by weight of the glycol.

9. In a process wherein ethylene glycol is heated as a liquid at anelevated temperature, the method of minimizing decomposition of theliquid which comprises maintaining dissolved therein from 0.2 to 5 percent by weight of quinoline. l

10. In a process wherein ethylene glycol is heated as a liquid at anelevated temperature,

the method of minimizing decomposition of the 2 comprises maintainingdissolved therein quinoline in a proportion oi from 0.2 to 5 per cent byweight of the glycol.

13. In a process wherein a liquid mixture of ethylene'glycol and alesser proportion of water is heated at an elevated temperature, themethod of minimizing decomposition of the liquid which comprisesmaintaining dissolved therein isoquinoline in a proportion of from 0.2to 5 per cent by weight of the glycol.

- 14. In a process wherein a liquid mixture of ethylene glycol and alesser proportion of water is heated at an elevated temperature, themethod of minimizing decomposition of the liquid which comprisesmaintaining dissolved therein quinaldine in a proportion of from 0.2 to5 per cent by weight of the glycol.

ARTHUR R. SEXTON. FRANCIS N, ADQUIST.

REFERENCES CITED The following references are of record in the file ofthis Patent:

UNITED STATES PATENTS Number Name Date 1,768,910 lhrig July 1, 19301,851,493 Calcott et a1. Mar. 29,1932 1,988,584 Dana et a1. Jan. 22,19352,068,868 Pier et a1. Jan. 26, 1937 2,078,256 Lieber et a1. Apr. 27,1937 2,130,924 Johnson et al. Sept. 20, 1938 2,136,788 Eairlie Nov. 15,1938 Y I FOREIGN PATENTS Number Country Date 702,565 France Jan. 26,1931

